Owing to their excellent characteristics, in particular their good thermal stability, chemical resistance and oil resistance, vinylidene fluoride (VdF)/hexafluoropropylene (HFP) copolymers, VdF/HFP/tetrafluoroethylene (TFE) copolymers and like fluoroelastomers (fluororubbers) produced by using VdF as an essential constituent monomer are used as the materials of various parts or members in such fields as the automobile, airplane and semiconductor industries where severe use conditions, such as exposures to high temperatures and/or various chemicals, are unavoidable.
Several other polymers comprising VdF as a constituent unit are also known; thus, for example, Patent Documents 1 and 2 describe that polymers were obtained by copolymerizing VdF and 2,3,3,3-tetrafluoropropene.